Coupling 3D modelling and forward-inverse modelling of potential field data (gravity and magnetic data).

The 3D modeling of geological objects is often decomposed in two steps: i) delimitation of the boundaries of the units corresponding to the various geological formations or ore types; and ii) verification and estimation of these boundaries using geophysical data. A new approach using potential-field interpolators addressing the 3D modeling problem is used here (Ch.Lajaunie et al. 1997). We will discuss how we can statistically estimate the validity of such 3D model taking in account various geophysical data. This estimation can be computed by inverting complementary datasets, provided (a) the data are a function of the 3D distribution of a source, (b) the response of a given 3D source distribution can be calculated, and (c) the source distribution shows some degree of correlation with the litho-regions. Gravity and magnetic potential field data generally satisfy these criteria. Unfortunately, these data do not allow source geometry to be uniquely resolved through inversion, nor is the source geometry likely to be perfectly correlated with the litho-regions. Even allowing for these limitations, we can see through the expression for the posterior probability density function (PPD) for a Bayesian inversion procedure how uncertainty in prior geological knowledge is modified by investigating the fit to observed potential field data for various models; (1) where is a normalizing constant, is the prior probability for the property model based on geological knowledge, and is the likelihood function that reflects the agreement between the observed potential field response and the predicted response of the model. Litho-models that have reasonable probability based on prior knowledge are downgraded if the likelihood deduced from the associated potential field response is very low. To reduce the non-uniqueness, we can add to the classical data, the tensor components of the field. The main goal with gradients measurements is to improve accuracy and spatial resolution of gravity and magnetic surveys. For those reasons, we propose to build a 3D forward modelling and inversion method for tensor data

Rates of Viral Evolution Are Linked to Host Geography in Bat Rabies

Rates of evolution span orders of magnitude among RNA viruses with important implications for viral transmission and emergence. Although the tempo of viral evolution is often ascribed to viral features such as mutation rates and transmission mode, these factors alone cannot explain variation among closely related viruses, where host biology might operate more strongly on viral evolution. Here, we analyzed sequence data from hundreds of rabies viruses collected from bats throughout the Americas to describe dramatic variation in the speed of rabies virus evolution when circulating in ecologically distinct reservoir species. Integration of ecological and genetic data through a comparative Bayesian analysis revealed that viral evolutionary rates were labile following historical jumps between bat species and nearly four times faster in tropical and subtropical bats compared to temperate species. The association between geography and viral evolution could not be explained by host metabolism, phylogeny or variable selection pressures, and instead appeared to be a consequence of reduced seasonality in bat activity and virus transmission associated with climate. Our results demonstrate a key role for host ecology in shaping the tempo of evolution in multi-host viruses and highlight the power of comparative phylogenetic methods to identify the host and environmental features that influence transmission dynamics

Regulation of polarized morphogenesis by protein kinase C iota in oncogenic epithelial spheroids.

Protein kinase C iota (PKCι), a serine/threonine kinase required for cell polarity, proliferation and migration, is commonly up- or downregulated in cancer. PKCι is a human oncogene but whether this is related to its role in cell polarity and what repertoire of oncogenes acts in concert with PKCι is not known. We developed a panel of candidate oncogene expressing Madin-Darby canine kidney (MDCK) cells and demonstrated that H-Ras, ErbB2 and phosphatidylinositol 3-kinase transformation led to non-polar spheroid morphogenesis (dysplasia), whereas MDCK spheroids expressing c-Raf or v-Src were largely polarized. We show that small interfering RNA (siRNA)-targeting PKCι decreased the size of all spheroids tested and partially reversed the aberrant polarity phenotype in H-Ras and ErbB2 spheroids only. This indicates distinct requirements for PKCι and moreover that different thresholds of PKCι activity are required for these phenotypes. By manipulating PKCι function using mutant constructs, siRNA depletion or chemical inhibition, we have demonstrated that PKCι is required for polarization of parental MDCK epithelial cysts in a 3D matrix and that there is a threshold of PKCι activity above and below which, disorganized epithelial morphogenesis results. Furthermore, treatment with a novel PKCι inhibitor, CRT0066854, was able to restore polarized morphogenesis in the dysplastic H-Ras spheroids. These results show that tightly regulated PKCι is required for normal-polarized morphogenesis in mammalian cells and that H-Ras and ErbB2 cooperate with PKCι for loss of polarization and dysplasia. The identification of a PKCι inhibitor that can restore polarized morphogenesis has implications for the treatment of Ras and ErbB2 driven malignancies.Cancer Research UK; Royal Marsden/Institute of Cancer Research National Institute for Health Research Biomedical Research Centre (M.L.)

3D GeoModelling for a Democratic Geothermal Interpretation

International audienceGeothermal exploration aims at locating favourable areas for exploitation. To reach this goal, various disciplines are implemented. Among the most common ones are geology, geophysics and geochemistry. Data are generally acquired in the field, such as geological observations, gravimetric surveys or thermal sources sampling. These data are interpreted to characterize the geometry, and the properties of the studied zone. They provide separate but complementary information to understand the area explored. However, combining geological, geophysical and geochemical interpretations is not an easy task. In such a context, one of the main difficulties lies in how to mix all the information to infer a coherent geothermal conceptual model. Merging them in the same space can help their combination to lead to a consistent understanding. First of all, this methodology allows to check the location of separate figures and to ensure their coherence. Moreover, it makes possible to build an overall interpretation based on various information. GeoModelling in 3-dimensions is an interesting candidate for this job because it allows to input materials from various origins to achieve an interpretation of the geothermal area. GeoModelling provides a common platform for interpretation during the exploration phase of a geothermal project. The final model can be completed through successive stages bringing new information at each step. For instance, a preliminary 3D geomodel can be based on very rough data from bibliography, even before any field work dedicated to the exploration. In a second time, geological data can be observed on the ground and incorporated in the model to refine the interpretation. The process can be continued using a gravimetric survey to improve the model at depth. Then, magnetotelluric resistivity can be injected in the model to infer possible fluid occurrence. Finally, location and properties of geothermal springs can be displayed in the 3D model to complete the interpretation. This kind of interdisciplinary workflow leads to a coherent geomodel filled by geology, geophysics and geochemistry. Making a 3D geomodel by associating complementary interpretations is an interesting perspective but giving the experts of each discipline the opportunity to interact in a democratic process is even more powerful. Indeed, geological, geophysical, and geochemical interpretations are not disconnected. Even if a preliminary work has to be carried out separately by each discipline, the interpretation coming from one can be fed by the others instead of putting them one after the other in a sequential workflow. To do so, the methodology has to be object oriented, where the central object is the 3D geomodel. In this light, the 3D model benefits from a common interpretation implemented jointly by geologists, geophysicists and geochemists. In other words, they can compare, connect, discuss, and adapt their own approaches for a mutual result in a GeoModelling environment. At the end, the conceptual model is not a conglomerate of distinct interpretations but a consensus shared by the contributors. The methodology described above is illustrated with two examples. These case-studies show how 3D GeoModelling is helpful to infer a democratic interpretation during the exploration phase. Beyond the interpretation for exploration, the geomodel can be enhanced during the next phases, when new data are acquired, to provide an up-to-date image of the investigated region. Such a 3D model can also be used to mesh the geometry of the zone and to compute dynamic simulations

3D cartographic modeling of the Alpine Arc

We built a 3D cartography of the alpine arc, a highly non-cylindrical mountain belt, using the 3D GeoModeller of the BRGM (French geological survey). The model allows to handle the large-scale 3D structure of seventeen major crustal units of the belt (from the lower crust to the sedimentary cover nappes), and two main discontinuities (the Insubric line and the Crustal Penninic Front). It provides a unique document to better understand their structural relationships and to produce new sections. The study area comprises the western alpine arc, from the Jura to the Northwest, up to the Bergell granite intrusion and the Lepontine Dome to the East, and is limited to the South by the Ligurian basin. The model is limited vertically 10 km above sea level at the top, and the moho interface at the bottom. We discarded the structural relationships between the Alps sensus stricto and the surrounding geodynamic systems such as the Rhine graben or the connection with the Apennines. The 3D-model is based on the global integration of various data such as the DEM of the Alps, the moho isobaths, the simplified geological and tectonic maps of the belt, the crustal cross-sections ECORS-CROP and NFP-20, and complementary cross-sections specifically built to precise local complexities. The database has first been integrated in a GIS-project to prepare their implementation in the GeoModeller, by homogenizing the different spatial referencing systems. The global model is finally interpolated from all these data, using the potential field method. The final document is a new tri-dimentional cartography that would be used as input for further alpine studies

Geothermal Systems: Interdisciplinary Approaches for an Effective Exploration

International audienc

Les atouts énergétiques du bassin de la Loire

La Loire et ses affluents contribuent à la production d'électrique d'origine nucléaire, hydraulique et thermique et au stockage de gaz en aquifère profond. Le bassin de la Loire offre en outre des conditions géologiques favorables au développement de la géothermie. Les volcans récents du nord du Massif Central offrent des perspectives pour la production d'électricité alors que les aquifères sédimentaires profonds sont portés à des températures adaptées à la production de chaleur. Quant aux roches profondes du socle hercynien, supportée par la technologie EGS (Enhanced Geothermal System), elles pourraient être propices à une production combinée d'électricité et de chaleur